This invention relates generally to a projection type liquid crystal display (LCD) system, such as projection video or television systems, and more particularly to a polarization converter for projection type LCD systems and the optical arrangement or optics system for projection type LCD system that provides for enhancement of the brightness in the system without increase in power consumption.
FIG. 13 illustrates a conventional projection type liquid crystal display, which figure is taken from Japanese Patent Laid-Open No. 63-185188. In FIG. 13, front linear polarizer 44 receives a light from a white light source 1 to select a linearly polarized light component between either the P-polarized light component and a S-polarized light component. Linearly polarized light is required for the illumination optics of the liquid crystal optics system. Spectroscopic dichroic mirror 45 separates light transmitted from polarizer 44 into the three primary colors of red, green and blue. The red color component, R, is directed in a straight path and the reflected by light reflectors 46. The green light component, G, is directed in a straight path without any change in direction. The blue light component, B, is directed in a straight path and then reflected by light reflectors 46. The three light components are light-modulated by respective liquid crystal light valves 8R, 8G and 8B. Dichroic prism 47 synthesizes the modulated light beams and then directs the beams onto rear linear polarizer 48. Polarizer 48 reselects the desired polarized light component, such as the S component, to obtain a resultant picture image that is enlarged by projection lens 49 onto projection screen 13.
In this type of conventional projection type liquid crystal display system, 50% or more of the light from light source 1 transmitted through polarizer 44 will be absorbed and lost, i.e., one polarized light component will be selected from the light and transmitted through polarizer 44 while the other polarized light component is absorbed in polarizer 44. Moreover, the necessary and desired level of brightness for such an LCD system cannot be provided with polarizer 44 having even 80% transmittance in spite of the employment of a light source having a high luminance intensity. As a result, the low light utilization efficiency of the light sources in such projection type LCD systems results in a dark projection screen which is not commercially acceptable to consumers.
Furthermore, polarizer 44 placed in close proximity to light source 1 is affected by heat absorption, which hinders the stable reliability of the projection type liquid crystal display under a wide range of ambient operating temperatures as well as may deform the shape of the polarizer. A high revolution type cooling fan with high cooling capability is, therefore, required to retain the stable reliability of the system. However, such high revolution type cooling fan generates considerable system noise and vibration so that a high resolution projection type LCD system commercially applicable for the consumer use cannot be achieved with good results.
More recently, polarization converters have been suggested for use in liquid crystal projectors wherein both polarization light components are brought into the same polarization direction by means of several prisms. See, for example, M. Imai et al., "Polarization Converter for Very Bright Projection Optics System of Liquid Crystal Projector", Institute of Electronics, Information and Communication Engineers, Part 5, 1989 Autumn National Convention Record, page 5-34, September, 1989 (published by Electronics). However, such prism systems are complex, difficult to assemble, competitively expensive and can lack compactness relative to the desired size of optics systems for a LCD projector system.
Thus, there is a need to develop brighter projection type LCD systems using compact optic elements and providing enhanced commercial applicability relative to cost, reliability and resultant image resolution and clarity.
It is an object of this invention to enhance the brightness of projection type LCD systems without increasing the system power consumption.
It is another object of this invention to provide for enhanced use of a light source employed in a projection type LCD system.
It is another object of this invention to provide a polarization converter for efficiently utilizing the light intensity of a light source in a projection type LCD system.
It is another object of this invention to provided an optics arrangement in a projection type LCD system that brightens the projected image created by the system optics while reducing the power consumption necessary for operation of the projection type LCD system.
It is another object of this invention to provide a projection type LCD system which is able to produce a high intensity picture image by utilizing maximum light flux from the light source, to provide high reliability under a wide range of ambient temperatures, and to achieve sufficiently low level noise and vibration rendering the system highly applicable for commercial audio/video projection type systems.